The widespread use of mobile terminals and so forth in recent years has brought demands for improved security between a transmitting apparatus and receiving apparatus when performing radio communication. One example of a conventional secure communication method that assures security (Patent Literature 1) will be described using FIG. 1.
In FIG. 1, a transmitting apparatus 10 has a modulation section 11, a radio section 12, and a transmitting antenna 13. Modulation section 11 has a transmit digital signal as input, modulates this signal and generates a transmit baseband signal, and outputs this signal to radio section 12. Radio section 12 has the transmit baseband signal as input, up-converts this signal and generates a transmit signal, and transmits this signal from transmitting antenna 13 as a radio signal.
On the other hand, a receiving apparatus 50 has a receiving antenna 51, a transmitting antenna 52, a radio section 53, an interference wave generation section 54, an interference wave processing section 55, an adding section 56, and a demodulation section 57. Radio section 53 has a received signal received by receiving antenna 51 as input, down-converts this signal and generates a received baseband signal, and outputs this signal to adding section 56. Radio section 53 also has an interference wave signal generated by interference wave generation section 54 as input, up-converts this signal and generates a transmit interference wave signal, and transmits this signal from transmitting antenna 52 as a radio signal. As a result, a signal in which the transmit signal transmitted as a radio signal from transmitting antenna 13 and the transmit interference wave signal transmitted as a radio signal from transmitting antenna 52 are added together becomes the received signal received by receiving antenna 51.
Interference wave processing section 55 has an interference wave signal generated by interference wave generation section 54 as input, performs phase inversion processing and attenuation processing on this signal and generates a processed interference wave signal, and outputs this signal to adding section 56.
Adding section 56 has the received baseband signal and processed interference wave signal as input, and adds these signals together. By this means, the interference wave signal is eliminated from the received baseband signal, and an interference wave free signal is generated. Adding section 56 outputs the interference wave free signal to demodulation section 57. Demodulation section 57 has the interference wave free signal as input, demodulates this signal, and outputs a received digital signal.
Thus, with the conventional technology, secure communication is performed by having an interference wave generated by the receiving apparatus and eliminating the interference wave in the receiving apparatus.    Patent Literature 1: Unexamined Japanese Patent Publication No.2001-94536